Already previously disclosed is the use of different types of cathode screens in compact fluorescent lamps with a view to obtaining various benefits and achieving an extended service life. The compact fluorescent lamp described in U.S. Pat. No. 4,952,187 offers a proposed solution as to how the service life can be further extended. This compact fluorescent lamp comprises spaces produced by constrictions of the fluorescent lamp body around the electrodes. Inside these spaces, emission materials are kept concentrated so that they fall back onto the electrode surface of the electrode in conjunction with phase shifting. This constriction (narrowing) is associated with a small negative space charge, whereby the released ions remain inside the space and are able to fall back onto the electrode surface. It has been found that the electron concentration increases when the electrode functions as an anode, that the anode fall is reduced, and that the temperature and rate of vaporization of the emission material are lowered, which brings an increased service life.
Compact fluorescent lamps produce a lot of light in relation to their size and also have a high discharge current and high cathode wear in relation to their external geometry. Because of the compact dimensions of the compact fluorescent lamps, this presents difficulties in finding sufficient space for bulky electrodes/cathodes. This means that it is difficult to achieve a long service life.
One problem associated with previously disclosed compact fluorescent lamps, however, is that the cathode space in these does not permit the use of larger electrodes in order to achieve a longer service life. Likewise, previously disclosed compact fluorescent lamps with a constricted tube body are associated with an uneconomical production process.
The applicants for the present invention currently produce and sell fluorescent lamps, which in most cases are powered at high frequency. The fluorescent lamps comprise a cathode space in accordance with Swedish patent SE 542 397. The cathode space according to this patent is formed by a cathode screen in the form of a cup, which is insulated from an electrode contained in the cathode space. Fluorescent lamps of this kind contain two cathode spaces, that is to say two electrodes which operate alternately as cathodes and anodes respectively. The service life of the electrode is limited by the vaporization and sputtering (atomization) of emitter material from the “hot point” of the electrode. This “hot point” derives its heat in the first instance from the ohmic heating and the kinetic energy of incident positive ions. Electron emission takes place from this point. Vaporization and sputtering of emitter material from the hot point means that ionized barium, strontium and calcium will be present at their highest concentration in the immediate vicinity of, and a few millimetres from the “hot point”. The object of the cathode screen is to increase the concentration of positive ions and in particular the ionized emitter material in the immediate vicinity of the “hot point” of the electrode.
The cathode space described in SE 542 397 functions very satisfactorily and is accordingly used in fluorescent lamps of the high-frequency type, although a further development of the same according to an embodiment of the present invention has brought with it improvements in respect of the adaptation of the cathode space for compact fluorescent lamps.
One aspect of the present invention is to make available a compact fluorescent lamp, which overcomes the disadvantages associated with the prior art and is a further development of, and an improvement to the compact fluorescent lamp described in U.S. Pat. No. 4,952,187.
The above-mentioned problem has been solved with the help of the compact fluorescent lamp described herein. One example includes a screened space formed by an internal wall of the fluorescent lamp body enclosing the electrode and by adjacent the electrode and beyond it in a direction away from a contact end, a disc-shaped cathode screen, containing a central opening. Other purposes and advantages can be appreciated from the accompanying disclosure including the drawings.
The compact fluorescent lamp can thus be made to take up as little space as possible, at the same time as appropriate conditions are created for imparting a long service life to the compact fluorescent lamp. The electrode can be made larger by means of the indicated distinctive features, in conjunction with which a larger quantity of emitter material can be applied to the electrode. All types of compact fluorescent lamp appropriately include two electrodes at the foot part of the fluorescent lamp body or bodies, and a disc-shaped cathode screen is appropriately arranged next to both electrodes. Compact fluorescent lamps can be of the type with 2, 4 or 6 bars and 2 or 4 pins for electrical connection. By the expedient of causing the electrode to correspond essentially to the average internal diameter of the fluorescent lamp body, although with a slightly smaller extent (so that electrical contact does not occur), the electrode can be executed so that it is larger and/or longer than permitted by the prior art, as a consequence of which its service life can be extended at the same time as the internal diameter of the fluorescent lamp body is retained, but without the compact fluorescent lamp itself needing to be made larger. Likewise, the manufacture of the compact fluorescent lamp can be achieved in an economical manner, because there is no longer a requirement for constriction of the fluorescent lamp body to be performed in a complicated stage of the manufacturing process.
A second electrode is so arranged that it is screened by means of a second, disc-shaped cathode screen, in an embodiment.
Alternatively, the distance between the electrode and the cathode screen is the smallest possible without causing contact to occur.
The cathode screen can thus be electrically insulated from the electrode, and the functionality can be maintained. The area closest to the electrode in the cathode space exhibits the highest concentration of ionized emitter material. The service life of the electrode is increased by the return migration of vaporized emission material that takes place from the screened space. Ionized barium and strontium atoms become electrically charged and are attracted back to the negatively charged cathode. The screened space is formed by the underside of the disc-shaped cathode screen and the internal wall of the fluorescent lamp body (its internal wall around the electrode essentially from the position of the electrode to the disc-shaped cathode screen).
The distance between the electrode and the disc-shaped cathode screen is appropriately 4-8 mm, and preferably 5-7 mm.
The distance between the electrode and the internal wall of the fluorescent lamp body is appropriately 1-4 mm, and preferably 2-3 mm.
This means that ionized emitter material is present at its highest concentration in the immediate vicinity of, and for a few millimetres outwards from the hot point. The electrode is provided with emitter material, which possesses the ability to emit electrons in the presence of a moderate temperature and energy supply. The emitter material contains alkali oxides. The service life of the electrode is limited by the vaporization and sputtering of emitter material from the “hot point” of the electrode. The hot point of the electrode obtains its heat primarily from the electrical heating and the kinetic energy of incident positive ions. The electron emission takes place from this hot point of the electrode. It has been shown by experiment that the disc-shaped cathode screen together with the internal wall of the fluorescent lamp body, that is to say the wall area that encloses the electrode as far as the disc-shaped cathode screen, increases the concentration of positive ions and in particular the ionized emitter material in the immediate vicinity of the hot point of the electrode, that is to say when the distance between the electrode and the disc-shaped cathode screen is 4-8 mm, and preferably 5-7 mm.
The disc-shaped cathode screen preferably has an extent essentially corresponding to the internal cross-sectional area of the fluorescent lamp body, viewed in a plane perpendicular to the essential longitudinal direction of the fluorescent lamp body within the area of the cathode space, but without coming into electrical contact with the fluorescent lamp body. The disc-shaped cathode screen is supported by a support device (such as a metal stay fused into a foot) and is electrically insulated from the electrode.
In this way, the underside of the disc-shaped cathode screen together with the internal wall of the fluorescent lamp body, that is to say the wall area that encloses the electrode as far as the disc-shaped cathode screen, forms a screened space.
Alternatively, the central opening has a diameter of 4-8 mm, and preferably 5-7 mm.
The central opening through the cathode screen brings about a “compression” of the fluorescent lamp plasma with increased current concentration/electron concentration. The increased current concentration in the vicinity of the cathode increases the chance of vaporized emitter material being ionized in the immediate vicinity of the cathode, which in turn gives an improved “return migration” of emitter material to the cathode. The increase in the current concentration adjacent to the hot point of the cathode also reduces the cathode voltage drop and the wear/heating caused by incident positive ions to a certain extent. One consequence of the “compression” of the fluorescent lamp plasma is that the presence of ions (ionized emitter material) and, for example, mercury outside the cathode screen, for example 10 mm from the electrode, will also be reduced steeply in comparison with a design without a cathode screen.
The side of the disc-shaped cathode screen facing away from the electrode appropriately exhibits a rounded area.
Assembly of the disc-shaped cathode screen can take place more rapidly in this way, and can be performed by automatic means, since the introduction of this into the fluorescent lamp body is simplified at the same time as the risk of damage to the layers of luminescent powder on the internal wall of the fluorescent lamp body in conjunction with its introduction is reduced.
The side of the disc-shaped cathode screen facing towards the electrode preferably exhibits a concave surface.
The rounded area produced on the other side can thus be utilized as a concave surface facing towards the electrode. This simplifies manufacture, because a flat metal blank can be stamped out to the desired form, thereby producing both the rounded area and the concave surface, which concave surface helps to prevent the fluorescent lamp plasma and the current transport through the fluorescent lamp gas from passing close to the internal wall of the fluorescent lamp body, on the outside of the cathode screen, and in so doing from being concentrated into the central opening of the cathode screen.
Alternatively, the disc-shaped cathode screen is made of metal.
The metal is iron in an embodiment. A disc-shaped cathode screen, which has an almost non-existent tendency to react with the components of the fluorescent lamp atmosphere, has thus been produced in this way, in conjunction with which chemical impurities, the effect of which could be to impair the function of the emitter material in the cathode space, are avoided. The disc-shaped cathode screen can appropriately be manufactured in a single piece and in a single operation by means of the pressing/stamping of a metal blank, such as iron, nickel, etc.
The disc-shaped cathode screen is appropriately supported by a support device that is electrically insulated from the electrode.
The disc-shaped cathode screen can be made insulated in this way.
Alternatively, the disc-shaped cathode screen is supported by at least two support devices that are electrically insulated from the electrode.
This ensures that the disc-shaped cathode screen is retained in a central position in the fluorescent lamp body without coming into contact with the internal wall of the fluorescent lamp body and any layer of luminescent powder applied thereto (luminescent material layer). Likewise, the disc-shaped cathode screen can be executed in this way with an optimal extent in relation to the internal diameter of the fluorescent lamp body.